1. Field of the Invention
This invention relates to direct current to alternating current power converters, and more specifically, to a direct power converter having bipolar output and bidirectional reactive current transfer.
2. Description of the Related Art
Power converters transform direct current, unipolar, energy to alternating current, bipolar, energy, or perform the reverse transformation. Generally, however, both functions cannot be performed at the same time. Unfortunately however, when the load on the ac output of a converter is reactive in nature, i.e. other than purely resistive, a reverse current condition can occur due to the capacitive or inductive reactive load. And because diodes are generally present in the power flow path of dc to ac power converters the diodes will block any attempted reverse current flow from a reactive load back into the actual dc power source. Therefore when reactive loads are present, energy is wasted in the power converter as the reactive load's reverse current flow is blocked resulting in component heating, power losses and inefficiencies. Furthermore, even among those power converters that state that they return power to the source, when the output voltage Vout is .ltoreq.Vin, the source, power typically is not returned to the source.
Additionally, in the case of unipolar dc to bipolar ac power converters, complex control circuits having feedback control are required in order to achieve linear proportional control of the output value and polarity. And in the case of reverse power flow as above, an inability to control the output voltage is prevalent. Moreover, many converters that utilize switching circuitry have problems with cross over distortion.
Furthermore, in many unipolar dc to bipolar ac power converters, a problem that causes efficiency losses and possible component damage exists. Power converters by their nature use switches, mechanical or solid state to create the desired ac. In many dc power converters there may be current flowing in the switches at the time that the switch turns OFF. This sudden current cutoff can cause large voltages to be induced into the power converter circuitry which leads to circuit damage and loss of efficiency.
Therefore a need existed for a power converter to transform direct current, unipolar, energy to alternating current, bipolar, energy having a feature of returning reactive energy back to the source in the presence of a reactive load for improved energy efficiency.
Another need existed for a power converter to transform direct current, unipolar, energy to alternating current, bipolar, energy having a feature of returning energy to the source even when the output voltage Vout is .ltoreq.Vin, the source.
A further need existed for a power converter to transform direct current, unipolar, energy to alternating current, bipolar, energy having a feature of a simple control circuit without feedback control that achieves linear proportional control of the power converter output value and polarity, while also possessing no cross over distortion.
Yet another need existed for a power converter to transform direct current, unipolar, energy to alternating current, bipolar, energy having a feature whereby switches are not interrupting reverse power flows thus preventing component damage and providing increased energy efficiency.